When forming elongated, hollow articles of fiber-reinforced composite material, such as hollow beams or the like, a metallic core or bar is often used as a mandrel or tool, around which a plurality of layers of a resin-impregnated filament is applied by winding it in an overlapping manner to form a laminated, semi-finished article. After curing of this composite article in a subsequent heat-treatment step, e.g. in an oven or autoclave, the cured article is cooled together with the tool bar. In the cooling phase, normally in room temperature, the tool bar shrinks to a certain degree, i.e. the cross-sectional area and the length of the tool bar is somewhat reduced, whereas the dimensions of the cured article remain substantially unchanged. In some cases, especially where the article and the tool bar are slightly curved in one or two directions and have a lengthwise tapered configuration, the shrinkage of the tool bar may cause undesired engagement between the tool bar and the cured article at certain locations along the tool bar due to uncontrolled mutual longitudinal movements of the tool bar and the article during the cooling phase. This may irrevocably damage the article at certain locations when dismantling the same from the tool bar.